1. Field of the Invention
The present invention relates to an ink jet recording apparatus which performs recording by ejecting ink.
2. Description of the Related Art
Recording apparatuses which perform recording on recording medium such as paper, transparent films for over head projectors, or the like (these are called "recording paper", or simply "paper" hereinafter) are proposed in a number of forms that mount various types of recording heads. For example, recording heads such as wire dot heads, thermal heads, ink jet heads, are used in serial printers. In particular, ink jet printers attract attention owing to their low running cost and low operation noise resulting from the fact that they eject ink directly on the recording paper.
Today, ink jet recording apparatuses, and in particular, recording heads are fabricated by the film-forming technique or micro-processing technique used for manufacturing semiconductor devices. As a result, fabrication of small-sized and inexpensive recording heads are being implemented, and removable type recording heads, which include an ink reservoir as their integral part, are proposed. This also makes it possible to produce recording apparatuses of small-sized, simple construction.
The ink jet recording apparatuses having these various advantages are being widely used as recording devices of such apparatuses as electronic typewriters, word processors, facsimiles, copying machines, or the like. The ink jet recording apparatuses are provided with arrangements suitable for functions and operation types of each of these apparatuses.
Furthermore, there has been recent trend that small-sized, light, portable electronic typewriters or word processors are becoming more and more popular. In view of these points, demand for small-sized, simple construction ink jet recording apparatuses is increasing.
In the ink jet recording apparatuses, sizes of ink dots formed on recording paper are a major factor for determining the density of images. The quality of images also depends on the accuracy of the position of dots. From these points of view, control of the projectile length of drops of ink ejected from the recording head, namely, the distance between the recording head and the recording paper (called "gap" below) is a major issue.
In addition, a variety of recording media are used because of the wide range of machines that use the ink jet recording apparatuses, and of the attribute that it performs recording by adhering drops of ink on the media. As a result, the ink jet apparatuses must adjust the gap in response to the kind of media, particularly to the thickness thereof.
As a gap adjusting mechanism, is known an arrangement which adjusts the gap by letting a transport roller escape backward by pressing it with rollers mounted on a carriage on which a recording head is loaded, when rather thick recording paper is used. In this arrangement, however, the rollers must press the transport roller with large force so as to let the transport roller escape backward, thus, the moving resistance of the carriage increases because of the roller so that the torque of the motor for driving the carriage must be increased.
On the other hand, when the recording paper of common thickness is used, the following arrangements can be used: first, an arrangement that a transport roller is pressed to a paper pressure plate so as to escape for thick paper; second, an arrangement that the paper pressure plate is pressed by a carriage. These arrangements, however, pose problems that the arrangements become complicated, or that insertion of the recording paper between the paper pressure plate and the transport roller may become difficult in the case where the pressure between the paper pressure plate and the transport roller is not appropriate, or the pressure on the paper is not suitable because of the kind of materials of the paper, or of its thickness.
Alternatively, there is arrangement for adjusting the gap by rotating a carriage about a guide shaft thereof, or by shifting a recording head with regard to a carriage. The arrangement, however, has a disadvantage that the construction and operation for adjustment become complicated.
Generally, the ink jet recording apparatuses are provided with a system for ejection recovery processing for the recording head. More specifically, the recording head of the ink jet system may suffer from a ejection failure of ink because of increase in viscosity of ink, of clogging of the ejection outlets or the like. To prevent the failure, the ejection-outlet-disposed surface of the recording head is capped so as to prevent the water in the ink from vaporizing, or to remove the clogging by forcefully sucking the ink with the recording head being capped.
The capping operation is generally performed as follows: first, the carriage on which the recording head is mounted is moved to a predetermined position such as the home position; second, the cap, which is provided so that it can move back and forth, is pressed to the recording head; and the ink is sucked by the cap that covers with the recording head.
This arrangement poses a problem that when the carriage or the recording head is moved so that the recording head is covered by the cap, the recording head may escape from the cap, which hinders reliable capping. Such a problem occurs in other cases: for example, an apparatus having such construction in which a flexible blade wipes the ejection-outlet-disposed surface of a recording head while the recording head is moving so that drops of ink sticking to the ejection-outlet-disposed surface are removed, may suffer from a problem similar to the above problem when the blade makes contact with the ejection-outlet-disposed surface.
Furthermore, the ink jet recording apparatus may have such arrangement in which ejection outlets of a recording head are divided into several blocks so that the blocks are sequentially driven on time sharing basis. A serial type apparatus of this kind, which performs recording with the movement of the recording head, has a problem that a line to be recorded normal to the moving direction (the scanning direction) of the recording head, that is, a line in the vertical direction (the subscanning direction) is obliquely recorded without taking any additional steps.
To correct such an oblique line to a vertical line, is used such an arrangement that a part of a carriage bearing a recording head is inclined so that an ejection-outlet-array line consisting of a plurality of ejection outlets is inclined.
This arrangement, however, poses a problem that it is difficult to achieve the accuracy of the inclination. Furthermore, there are other problems: when the inclination must be altered in accordance with the ejection timing or carriage velocity, one form of carriage may be insufficient to deal with this alteration; a variety types of carriage must be prepared so that one of them is installed in the apparatus. Even if one form of carriage can deal with the alteration, configuration of the carriage for changing the inclination will become too complicated.